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Stevens Point, AZ, United States

Fletcher K.,The Game and Wildlife Conservation Trust | Howarth D.,The Game and Wildlife Conservation Trust | Kirby A.,The Game and Wildlife Conservation Trust | Kirby A.,AMEC Environment and Infrastructure Inc. | And 3 more authors.
Ibis | Year: 2013

Upland birds are predicted to be particularly vulnerable to the effects of climate change, yet few studies have examined these effects on their breeding phenology and productivity. Laying dates of Red Grouse Lagopus lagopus scotica in the Scottish Highlands advanced by 0.5 days/year between 1992 and 2011 and were inversely correlated with pre-laying temperature, with a near-significant increase in temperature over this period. Earlier clutches were larger and chick survival was greater in earlier nesting attempts. However, chick survival was also higher in years with lower May temperatures and lower August temperatures in the previous year, the latter probably related to prey abundance in the subsequent breeding season. Although laying dates are advancing, climate change does not currently appear to be having an overall effect on chick survival of Red Grouse within the climate range recorded in this study. © 2013 British Ornithologists' Union. Source

Lommler J.C.,AMEC Environment and Infrastructure Inc. | Bandini P.,New Mexico State University
Geotechnical Special Publication | Year: 2015

Collapsible soils are generally considered to be soils that settle upon wetting and loading. Settlement of collapsible soils is a common problem particularly in arid and semi-arid regions of the United States because these soils exist at very low moisture contents in their natural environment. Locally, geotechnical engineers refer to native soils that settle due to self-weight upon wetting as "collapsible soils" or "hydro-collapsible soils." This paper presents some observations and findings of a study on natural collapsible granular soils that formed in alluvial fans in central New Mexico. The paper describes the soil structure observed in microphotographs and scanning electron microscope images and the effects of sample disturbance on the prediction of soil collapse upon wetting from laboratory test results. The paper offers a hypothesis on the mechanism that could have produced some features of the structure of the collapsible soils in the area. © ASCE 2015. Source

Youngs R.R.,AMEC Environment and Infrastructure Inc.
Earthquake Spectra | Year: 2014

We present an update to our 2008 NGA model for predicting horizontal ground motion amplitudes caused by shallow crustal earthquakes occurring in active tectonic environments. The update is based on analysis of the greatly expanded NGA-West2 ground motion database and numerical simulations. The updated model contains minor adjustments to our 2008 functional form related to style of faulting effects, hanging wall effects, scaling with the depth to top of rupture, scaling with sediment thickness, and the inclusion of additional terms for the effects of fault dip and rupture directivity. In addition, we incorporate regional differences in far-source distance attenuation and site effects between California and other active tectonic regions. Compared to our 2008 NGA model, the predicted medians by the updated model are similar for M > 7 and are lower for M < 5. The aleatory variability is larger than that obtained in our 2008 model. © 2014, Earthquake Engineering Research Institute. Source

Johnson S.R.,AMEC Environment and Infrastructure Inc. | Johnson S.R.,North Carolina State University | Burchell M.R.,North Carolina State University | Evans R.O.,North Carolina State University | And 2 more authors.
Ecological Engineering | Year: 2013

Relatively narrow (<50m) riparian buffers strategically reestablished in correct landscape positions have been shown to significantly reduce agricultural non-point source pollution to streams. Because of this, conservation programs have been established to encourage landowners to enroll lands near surface waters to improve water quality. Former cropland enrolled in a conservation program was evaluated to determine its effectiveness in reducing nitrate-nitrogen (NO3--N) in shallow groundwater. This conservation buffer (CB) was up to 80m wide and was planted with loblolly pine (Pinus taeda). It was situated upslope of an existing 30-60m wide riparian hardwood forest buffer (EHB) located within the floodplain of an intermittent stream. Shallow groundwater NO3--N, groundwater hydrology, total organic carbon, and soil redox potential were measured throughout both the CB and the EHB for 18 months. Groundwater NO3--N concentrations, often 5-15mgL-1 within the CB, were not significantly reduced from concentrations that entered from the agricultural field edge. However, a decrease in NO3--N concentration was observed within the EHB (17-83%). The hydrology of the CB coupled with relatively low organic carbon contributed to a low denitrification potential and lack of NO3--N reduction compared with the EHB. While the CB enrollment likely provided additional habitat benefits it did not appear to provide treatment of groundwater NO3--N. It is our conclusion that landscape position is a more important defining variable for buffer site selection than buffer width if NO3--N reduction is a primary goal. © 2012 Elsevier B.V. Source

Bierman P.R.,University of Vermont | Coppersmith R.,Coppersmith Consultingm Inc. | Hanson K.,AMEC Environment and Infrastructure Inc. | Neveling J.,Council for Geoscience | And 5 more authors.
GSA Today | Year: 2014

Southernmost Africa, with extensive upland geomorphic surfaces, deep canyons, and numerous faults, has long interested geoscientists. A paucity of dates and low rates of background seismicity make it challenging to quantify the pace of landscape change and determine the likelihood and timing of fault movement that could raise and lower parts of the landscape and create associated geohazards. To infer regional rates of denudation, we measured 10Be in river sediment samples and found that south-central South Africa is eroding ∼5 m m.y.-1, a slow erosion rate consistent with those measured in other non-tectonically active areas, including much of southern Africa. To estimate the rate at which extensive, fossil, upland, silcrete-mantled pediment surfaces erode, we measured 10Be and 26Al in exposed quartzite samples. Undeformed upland surfaces are little changed since the Pliocene; some have minimum exposure ages exceeding 2.5 m.y. (median, 1.3 m.y.) and maximum erosion rates of <0.2 m m.y.-1 (median, 0.34 m m.y.-1), consistent with no Quaternary movement on faults that displace the underlying quartzite but not the silcrete cover. We directly dated a recent displacement event on the only recognized Quaternary-active fault in South Africa, a fault that displaces both silcrete and the underlying quartzite. The concentrations of 10Be in exposed fault scarp samples are consistent with a 1.5 m displacement occurring ca. 25 ka. Samples from this offset upland surface have lower minimum limiting exposure ages and higher maximum erosion rates than those from undeformed pediment surfaces, consistent with Pleistocene earthquakes and deformation reducing overall landscape stability proximal to the fault zone. Rates of landscape change on the extensive, stable, silcretized, upland pediment surfaces are an order of magnitude lower than basin-average erosion rates. As isostatic response to regional denudation uplifts the entire landscape at several meters per million years, valleys deepen, isolating stable upland surfaces and creating the spectacular relief for which the region is known. Source

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